This invention relates to a device for pushing printing sheet toward a printing assembly for use in a printing apparatus in which printing is applied to material made of metal sheet material such as aluminum plate and tin plate.
It has been a usual practice that material to be printed in the form of sheet (hereinafter referred to as printing sheet) has conventionally been transported between a blanket cylinder 55 and an impression cylinder 56 by a pusher means 57 in a general printing apparatus as shown in FIG. 5. The printing apparatus is provided with a container 51 for containing therein printing sheets, transport assembly 52 for transporting printing sheets dispensed one by one from the container 51, and printing assembly 53 includes a plate cylinder 54 for applying printing to the printing sheet transported thereto, blanket cylinder 55 and impression cylinder 56. The pusher means 57 is, as shown in FIGS. 6 and 7 illustrating an existing pushing device, provided with a pair of sprockets 61, chains 62, and sheet pushers 63. The pair of sprockets 61 are secured to the drive shaft 58 with spaced away from each other, and the chain 62 is wounded on each sprocket 61. The sheet pusher 63, mounted to the chain 62, pushes a rear end of the printing sheet to give additional force in transporting the printing sheet.
At one end of the drive shaft 58 are provided a clutch 64 which engages and disengages to permit and prohibit a transmission state of a drive transmission mechanism 60, coupling bolt 65 for holding the clutch 64 in its engaged state, and operation handle 66 for operably rotating the drive shaft 58. The drive transmission mechanism 60 includes a plurality of gears arranged so as to transmit the driving force of drive means 59 for drivingly rotating the impression cylinder 56 to the drive shaft 58. In such a case where the size of the printing sheet to be transported is charged, the coupling bolt 65 is unfastened to cause the clutch 64 to disengage, whereby to disconnect the impression cylinder 56 and drive shaft 58 from each other. Then, the drive means 59 causes the impression cylinder 56 to rotate so as to set at a reference position holders provided on a circumferential surface of the cylinder 56 for holding the printing sheet while an operating state of the drive means 59 is being detected by a rotary encoder 67. In addition, the drive shaft 58 is rotated by operating the operation handle 66 to adjust positions of the sheet pushers 63, so that a leading end of the printing sheet is positioned at the reference position. Thereby, the leading end of the printing sheet is held by the holders at an appropriate timing.
With the pushing device thus constructed, each time the size of printing sheet is to be changed, positions of the sheet pushers have to manually adjusted by rotating the operation handle, or other ways. This manual adjustment is very cumbersome. Further, in the case where a torque releaser mounted on the drive shaft operates to cause the position of the holders of the impression cylinder relative to that of the sheet pushers to change at an occurrence of jamming of the printing sheet, the above cumbersome adjustment has to be made.
It is an object of the print invention to provide a device for pushing printing material for use in a printing apparatus which has overcome the above drawbacks.